Specimen test slides and procedures for detecting occult blood in fetal matter are well known. For example, U.S. Pat. No. 3,996,006 discloses slides having a specimen receiving sheet between a front panel and a rear panel with openings in the front and rear panels and pivotal covers or flaps to cover these openings. One such test slide is sold under the trademark of `Hemoccult`.
The specimen receiving sheet is generally an absorbent paper impregnated with a guaiac reagent. The hemoglobin catalyzed oxidation of the guaiac extract coated paper is used clinically to detect occult blood in feces. Briefly, the test procedure is as follows.
A sample of fecal matter is smeared onto the guaiac paper through an opening of the front panel. The panel is then covered and the flap of the rear panel is opened. A developing solution such as hydrogen peroxide is applied to the guaiac paper via the corresponding opening in the rear panel. If blood is present in the fecal matter, the guaiac reaction will color the paper blue. The overall reaction is a follows: ##STR1##
One of the problems associated with this test is the number of false negatives, i.e., negative test results in samples of known bleeding patients. The test is not sensitive enough to pick up lower levels of blood in the feces.
Another disadvantage of the guaiac test is that other non hemoglobin type compounds present in the stool, such as peroxidases present in certain foods, will also catalyze the oxidation of guaiac and result in a blue color. This results in false positive reaction, i.e., a positive reaction without fecal occult blood present.
Previous attempts have been made to increase the sensitivity of the present Hemoccult.RTM. test. Hydration of the smear prior to development is often employed. However, while hydration produces a more sensitive test the method also adversely affects the specificity of the test. It produces unacceptable high false positive rates by reacting with other interfering substances such as vegetable peroxidases.
It is therefore the object of this invention to increase the sensitivity of the test while improving or maintaining the specificity of the current Hemoccult.RTM. test. Increasing the sensitivity includes detecting lower levels of blood in the feces and obtaining greater readability, i.e., obtaining a clearer and deeper blue color with the same concentrations.